Treatment of process water, wastewater and sludge

Based on our many years of experience in this field, Fraunhofer IGB offers both biological and physico-chemical methods and solutions for wastewater treatment and sludge conditioning for industry and municipalities.

A particular focus is on the design of new wastewater treatment plant concepts for a "wastewater treatment plant of the future" that not only treat wastewater in compliance with the regulations, but can also generate additional value at the same time – via the production of energy sources and products such as fertilizers to biostimulants for agriculture.

Our portfolio also includes customized membranes, filters and adsorbents, which will play important roles in the growing future markets for water and wastewater treatment systems.

Desalination and nutrient recovery

Electrodialysis.

Salts, if recovered in sufficiently pure form, can be directly reused as a valuable material. Since increased recycling increases the concentration of salts in process waste water, they must be increasingly removed before discharge.

Electrochemical (membrane) processes are suitable for the separation of salt ions. In these processes, only the charged particles from an aqueous solution are transported through the ion exchange membrane in an electric field. The separation processes can be economically integrated into the process chain for the recovery of valuable materials, the recycling of process auxiliaries and the treatment of wastewater.

The IGB has developed an electrochemical process for the recovery of inorganic nutrients from municipal, industrial and agricultural wastewater. This process precipitates nitrogen and phosphorus with a magnesium electrode as magnesium-ammonium-phosphate (struvite), a high-quality fertilizer.

Biological wastewater treatment for degradation of organic ingredients

Festbettreaktor
Fixed-bed circulation reactor.

Biological processes use the self-purifying power of ecosystems, in which those organisms that can degrade existing substrates most effectively prevail. A prerequisite is that the substrates are fundamentally biodegradable. Technical processes such as biomass retention ensure that these natural processes take place in a very small space and at a high intensity.

Fraunhofer IGB has developed various bioreactors for wastewater treatment, for example anaerobic and aerobic loop reactors (gas lift/air lift reactors), membrane bioreactors or a fixed-bed circulating reactor in which the particle bed is periodically circulated. We select suitable bioreactors and corresponding process concepts based on the specific requirements of the respective wastewater and the intended recycling and adapt them to regional, climatic and cultural conditions.

Membrane filtration processes and adsorption

Membrane adsorber REM.
© Fraunhofer IGB

In industry, membrane technology has also proven itself as a separation technology for the treatment of raw water to process water or for the purification of process waste water. They operate without phase change, and the equipment required is kept within limits. Further advantages are simple upscaling (modularity) and low chemical consumption.  

At Fraunhofer IGB, membrane materials, membranes and membrane processes are researched and developed for microfiltration (MF, suspended particles, bacteria), ultrafiltration (UF, macromolecules, viruses and colloids), nanofiltration (NF, organic compounds and divalent ions) and reverse osmosis (monovalent ions).

A new focus is on membrane adsorbers, which combine the advantages of membranes with those of adsorber materials. For this purpose, we equip membranes with special functional groups in order to specifically remove impurities such as heavy metal ions (Pb, Cd, Cu) or organic molecules (penicillin G, bisphenol A) from process wastewater by means of adsorption. Membrane adsorbers are also used for the concentration of solutions with low pollutant concentration, in order to subsequently treat the enriched solution energy-efficiently with AOP technologies and destroy the pollutant.

Physical-chemical processes

Batch reactor for UVC/H2O2 treatment of water.
Batch reactor for UVC/H₂O₂ treatment of water.

Advanced oxidation processes (AOP)

Oxidative water treatment (AOP, Advanced Oxidation Processes or AOT, Advanced Oxidation Technologies) is the term used to describe chemical treatment processes in which highly reactive hydroxyl radicals are used for the oxidation of water ingredients that are difficult to break down.

AOP processes are always used when biodegradation is not possible or not efficient, for example because the impurities contain persistent substances. Furthermore, AOP processes are the method of choice if the process wastewater has a toxic effect on the microorganisms of a biological treatment stage or if it is extremely discontinuous. In many cases, a process combination with a reductive partial degradation is also recommended as the most energy-efficient variant. The possibility of testing various combination treatments in the laboratory and pilot plant of the IGB is one of our unique selling points.

Electrophysical precipitation and coagulation with sacrificial anodes

In this process established at the IGB, the water to be treated is passed through a reactor in which an electric current flows through sacrificial electrodes. In the course of electrochemical reactions, the sacrificial electrodes dissolve, releasing their metal ions, and metal hydroxide flakes are formed. These have a high adsorption capacity and can bind to themselves finely distributed, non-sedimentable particles in the size range of a few micrometers or smaller. During the formation of hydroxide flakes, co-precipitation and inclusion precipitation reactions also occur, in which dissolved organic and inorganic substances are precipitated. The precipitated substances can be separated mechanically by sedimentation or filtration.

Electrophysical precipitation replaces conventional chemical flocculation precipitation techniques with the advantage that the flocculants are provided electrolytically from solid electrodes directly at the place of need in dissolved form and dosed according to need. As electrode material iron or aluminium from standard sheets can be used, which are inexpensive, always available and easy to handle. Only the metal ion is specifically added to the water to be treated, so there is no salting.

The EpF process is also particularly suitable for the splitting of stable emulsions, such as drilling and cutting oil emulsions or wastewater from washing processes, which is otherwise often done by adding splitting chemicals.

Thermal processes

Thermal water treatment processes such as heating, distillation and rectification (thermal separation) are widely used in industry and commerce. The advantage of these processes is that the technologies are often relatively simple and robust in design and the thermal energy supply can usually be realized without great effort by firing, process steam or electrical heating. On the other hand, thermal treatment processes are energy-intensive, which makes new technical solutions necessary in the course of responsible handling of energy resources and increasing cost pressure.

The aim of research and development at Fraunhofer IGB is therefore to realize efficient and cost-effective thermal treatment processes by optimizing and combining different processes in order to be able to use waste heat or solar-thermally generated heat. Processes for solar seawater desalination, the concentration of industrial wastewater and the recovery of solvents are examples of processes that are being worked on at Fraunhofer IGB.

Combination of different processes and system integration

Due to the complex composition of typical industrial process waters, efficient separation of substances in one step is usually not possible. By combining and integrating different processes, we develop efficient, coordinated solutions that are optimized in terms of selectivity and energy efficiency in their overall effect as a process chain.

Automation and autonomous operation

Wherever possible, we develop process concepts so that they can be operated flexibly and, for example, are suitable for standby operation, i.e. can be switched on and off at any time. Integration into existing plants and automation up to autonomous operation or remote control are possible. Where necessary, we integrate online analytics, for example for the continuous recording of organic carbon (TOC, Total Organic Carbon), in order to ensure demand-based and consequently energy-optimized processing.

The wastewater treatment plant as a biorefinery

High-load digestion at the Erbach wastewater treatment plant.
© Fraunhofer IGB
High-load digestion at the Erbach wastewater treatment plant.

The circular economy is considered a key strategy for conserving resources and achieving climate targets. The ingredients in wastewater can also be used – if it is treated in an appropriate manner.

High-load digestion enables utilization of wastewater ingredients

The prerequisite for the utilization of the various substances involves making them available: through concentration, separation and processing.

The technical basis for this is the high-load digestion process developed at the IGB and implemented in many cases at wastewater treatment plants. High-load digestion not only converts the sludge produced at a wastewater treatment plant into biogas as a regenerative source of carbon and energy, but also supplies sludge water and sludge digestion residues (digestate) as further usable material flows.